Display screen with a graphical user interface for a security system



FIG. 1 is a front view of a display screen with a graphical user interface for a security system showing my new design; and,

FIG. 2 is a second embodiment thereof.

The broken lines showing a display screen and elements of the graphical user interface illustrate portions of the article, and form no part of the claimed design. 

CLAIM The ornamental design for a display screen with a graphical user interface for a security system, as shown and described. 